1. Field of the Invention
The present invention relates to a stacked ultrasound vibration device configured to excite ultrasound vibration and an ultrasound medical apparatus including the stacked ultrasound vibration device.
2. Description of the Related Art
Among ultrasound treatment instruments configured to utilize ultrasound vibration to perform a coagulation/dissection treatment of living tissue, there is an ultrasound treatment instrument including an ultrasound vibrator using a piezoelectric transducer as an ultrasound vibration source in a handpiece.
Among the ultrasound vibrators, there is an ultrasound vibrator including piezoelectric elements configured to convert an electrical signal to mechanical vibration, and the piezoelectric elements are sandwiched between two block-shaped metal members serving as a front mass or a back mass. The piezoelectric elements and the metal members are integrated by some kind of method such as adhesion, and they integrally vibrate. Such an ultrasound transducer is called a Langevin transducer.
An example of a known method of integrating the piezoelectric elements and the metal members in the Langevin transducer includes a bolt clamped Langevin transducer in which piezoelectric elements are placed between two metal members. In the bolt clamped Langevin transducer, the piezoelectric elements and the metal members are firmly fastened by a bolt, and the entire piezoelectric elements and metal members integrally vibrate.
In general, lead zirconate titanate (PZT, Pb(ZrX, Ti1-X)O3) is used for the piezoelectric elements used in the bolt clamped Langevin transducer. A shape of the piezoelectric elements is processed into a ring shape, and the bolt is pushed and inserted into the inside.
Productivity and electromechanical conversion efficiency of PZT are high, and PZT has good characteristics as a piezoelectric material. Therefore, PZT is used in various fields of ultrasound transducers, actuators, and the like for a long time.
However, lead is used in PZT, and use of a non-lead piezoelectric material without using lead has been desired in recent years from the viewpoint of preventing adverse effects on the environment. An example of a known non-lead piezoelectric material with high electromechanical conversion efficiency includes lithium niobate (LiNbO3) piezoelectric single crystals.
A method of placing piezoelectric elements between metal blocks and integrally bonding the piezoelectric elements and the metal blocks has been conventionally known as a configuration for inexpensively realizing a Langevin transducer using lithium niobate. Particularly, when a brazing material such as a solder is used to bond the metal blocks and the piezoelectric elements without using an adhesive, the Langevin transducer can obtain better vibration characteristics than those of the adhesive.
However, a high temperature process is generally necessary to bond the metal blocks and the piezoelectric elements by a brazing material such as a solder. There is a problem that the piezoelectric elements with piezoelectric single crystals crack due to thermal stress at dissimilar material bonding portions that are parts where the metal blocks and the piezoelectric elements are bonded.
An example of a disclosed technique for solving the problem includes an ultrasound vibrator of Japanese Patent Application Laid-Open Publication No. 2008-128875. A technique is known in the conventional ultrasound vibrator, in which structures, such as grooves and depressions, are provided on a bonding surface of each metal block bonded with an adhesive to electrodes provided on both upper and lower surfaces of a piezoelectric transducer. Therefore, generation of a shear strain during drive is suppressed, and a dielectric loss on the bonding surface is reduced. Furthermore, in the technique, generation of a crack in the piezoelectric transducer is prevented, and a vibration mode is stabilized.